Laminated fiber-reinforced sheet of polymeric material

ABSTRACT

A RIGID SHEET OF A POLYMERIC MATERIAL HAVING LOOSE FIBERS DISPERSED THROUGHOUT THE SHEET AND RANDOMLY ORIENTED AND PREDOMINANTLY LYING IN THE PLANE OF THE SHEET IS PRODUCED BY FEEDING A HOMOGENEOUS DOUGH-LIKE MASS FORMED FROM A SOLUTION OR EMULSION OF THE POLYMERIC MATERIAL AND THE   LOOSE FIBERS INTO THE NIP BETWEEN TWO CALENDER BOWLS, ONE OF WHICH IS HEATED, AND BUILDING THE MATERIAL UP IN LAMINATIONS ON ONE OF THE BOWLS.

May 11, 1971 G. WICKER 5 LAMINATED FIBER-REINFORCED SHEET OF POLYMERICMATERIAL Original Filed June 15, 1965 ATTORNEY United States Patent3,578,547 LAMINATED FIBER-REINFORCED SHEET F POLYMERIC MATERIAL GeorgeLeonard Wicker, Lancashire, England, assignor to Turner BrothersAsbestos Company Limited, Manchester, England Application June 15, 1965,Ser. No. 464,149, now Patent No. 3,461,012, dated Aug. 12, 1969, whichis a continuation-in-part of abandoned application Ser. No. 237,195,Nov. 13, 1962. Divided and fl1is application Apr. 28, 1969, Ser. No.819,631

Claims priority, application Great Britain, Nov. 13, 1961,

40,520/61; June 15, 1964, 24,749/64 Int. Cl. B32b 5/16 US. Cl. 161-156 6Claims ABSTRACT OF THE DISCLOSURE A rigid sheet of a polymeric materialhaving loose fibers dispersed throughout the sheet and randomly orientedand predominantly lying in the plane of the sheet is produced by feedinga homogeneous dough-like mass formed from a solution or emulsion of thepolymeric material and the loose fibers into the nip between twocalender bowls, one of which is heated, and building the material up inlaminations on one of the bowls.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is a divisionof application S.N. 464,- 149 filed June 15, 1965, now Pat. No.3,461,012 which is in turn a continuation-in-part of application S.N.237,195, filed Nov. 13, 1962, now abandoned.

BACKGROUND OF THE INVENTION (1) Field of the invention The inventionrelates to laminated fiber-reinforced sheets of polymeric material.

(2) The prior art Rigid thermoplastic mouldings can advantageously bemade by moulding heated sheets of a thermoplastic material that is rigidat room temperature. Suitable thermoplastic materials for this purposeare or consist essentially of one or more of the polymers of styrene,methylmethacrylate and acrylonitrile and copolymers in which one ofthese monomers predominates. Many of these materials are available insheet form and can readily be converted into unreinforced mouldings.

Now for many purposes reinforced mouldings are required, and it isdesirable to introduce fibrous reinforcement into the thermoplasticmaterial. It is known to introduce asbestos or other fibers intoplasticized polyvinyl chloride to produce flexible tiles, butsatisfactory rigid sheets cannot be made by a similar process. Toproduce a reinforced rigid moulding of polystyrene or a similarthermoplastic material it has been necessary hitherto either toincorporate reinforcing fibers in the thermoplastic material and convertthis into pellet form, and then make the product by injection-mouldingthe pellets, or to impregnate wire mesh, glass cloth, glass mat orsimilar preformed reinforcement with the thermoplastic material.

SUMMARY OF THE INVENTION The present invention comprises as a novelproduct a rigid sheet composed of a polymeric constituent with fibersuniformly dispersed throughout it and predominantly randomly oriented inthe plane of the sheet. The polymeric constituent is based predominantlyon one or more of styrene, methylmethacrylate and acrylonitrile. In thesimplest case the polymeric constituent may be a single polymer, forexample polystyrene. It may also be a single copolymer, for example ofstyrene and butadiene, the styrene predominating, or of acrylonitrile,butadiene and styrene, the acrylonitrile and styrene togetherpredominating. Again it may consist of a polymer mixture, at copolymermixture or a poly-copolymer mixture. Examples of such mixtures arepolystyrene mixed with (or modified by) a styrene-butadiene copolymerand polystyrene mixed with (or modified by) a copolymer of styrene andmaleate ester.

It is of course well known that by varying the proportions of themonomers in a copolymer products with different properties are obtained,many copolymers of acrylonitrile and butadiene for instance, being of arubber-like nature and therefore flexible. Although the reinforcement isan important factor in imparting rigidity to the sheet, it is necessaryto ensure that if the polymeric constituent includes butadiene or othermonomer which tends to give a flexible copolymer the proportion of thatmonomer is so low that the polymeric constituent would, if notreinforced, be rigid or substantially rigid at room temperature.

Such sheets are suitable for moulding, but do suffer from thedisadvantage that they are inflammable. I have found that thefire-resistance of such sheets is greatly increased if the polymericconstituent is based additionally on a lesser proportion of a vinylchloride polymer, the vinyl chloride polymer preferably being a vinylchloride homopolymer, although it may also be a copolymer of vinylchloride with vinyl acetate or vinylidene chloride.

The vinyl chloride polymer is present in an amount of less than half thetotal amount of polymer constituent. It may comprise at least 10%, forexample from 10 to 49% of the total polymeric constituent, the remainderbeing based predominantly on styrene, methyl methacrylate oracrylonitrile, or more than one of these. I prefer that the amount ofpolymeric constituent should be about 50% of the total weight of thesheet in which case the vinyl chloride polymer comprises, say, from 10to 15% of the sheet. The sheets containing vinyl chloride polymer havegood fire retardance and the inclusion of vinyl chloride polymer 'withthe remainder of the polymeric constituent does not substantially affectthe strength properties of the sheets. The vinyl chloride polymer ispreferably unplasticized, since the presence of plasticizer may affectthe strength of the sheets.

Antimony oxide may be included in the sheets to improve fire retardancestill further.

It is desirable that in the sheet the proportion of the fibers should beas high as possible, and it is advantageously at least 20%. Thepolymeric constituent may be from 40 to of the total (sheet. Thesepercentages, and all others in this specificatidn, are by weight.

Inorganic fibers give better rigidity than organic fibers, and it istherefore preferable that the fibers should be wholly or predominantlyinorganic, say at least morgamc.

For moulding purposes, what is required is a sheet which can be readilymoulded to a desired shape. As the reinforcement is composed of fiberswhich can flow freely and individually in any direction during moulding(loose fibers), their movement is not restricted as is the case ofpreformed reinforcements such as woven cloths or mats.-

asbestos fibers of average length from 0.15 to 0.20 inch and choppedstaple glass fibers from 0.25 to 1.0 inch are suitable. Mixtures ofshort fibers with varying proportions of longer fibers, say, up to 2inches, may also be used and their use makes it possible to increase thestrength properties without materially reducing the mouldability. Thelonger fibers may be asbestos, glass or organic. Broadly there may befrom 80 to 100% inorganic fibers less than 1 inch long and from tofibers between 1 and 2 inches long.

The method of manufacture of the sheets is an important feature of theinvention. This method comprises converting the polymeric constituent inliquid form and the fibers into a substantially homogeneous dough-likemass, building up the mass in laminations into a sheet on a hot calenderbowl, cutting the sheet thus formed on the bowl and removing it from thebowl, and allowing it to cool to a rigid sheet.

One reason Why the polymeric constituent is used in liquid form is thatotherwise it would have to be melted and the high viscosity of the melt,which causes high shear forces during the mixing, would result in damageto the fibers. Another reason is that in building up the sheet on thehot calender bowl it is necessary that successive laminations shouldadhere to one another, and it is found that only by the use of theliquid form of the polymeric constituent can good adhesion be obtained.Moreover, in forming the dough-like compound it is important to wet allthe fibers, and this can be done by introducing the polymericconstituent in liquid form. The liquid may be an aqueous emulsion(conveniently a latex) or an organic solution. Emulsions of polystyreneand the other polymers and copolymers are available on the market. Anyvolatile constituent of the emulsion or solution will be removed in thehot-calendering or in the mixing.

Rigid sheets in which the polymeric constituent is based predominantlyon styrene but also contains some polyvinyl chloride are particularlyuseful. However, compatibility between molten polystyrene and moltenpolyvinyl chloride is notoriously poor and the normal calenderingtechnique in which a sheet is formed from a molten mix, which in thiscase would be of polystyrene and polyvinyl chloride, and compressed downto a thin sheet does not yield a homogenous sheet. The adoption of themethod of lamination described permits homogeneous sheets of reinforcedpolystyrene containing a minor proportion of polyvinyl chloride to bemade. The method is, of course, also applicable to the production ofsheets in which any other polymeric constituent based predominantly onstyrene, methylmethacrylate or acrylonitrile or more than one of theseand a minor proportion of vinyl chloride is used.

In carrying out the invention it is important to ensure that thesuccessive laminations adhere well during the calendering and that atough, strong sheet is formed. At the same time the sheet formed on thecalender bowl must not stick to the bowl. Water present in the emulsionserves as a release agent to prevent excessive adhesion of the sheet tothe calender bowl, but also reduces the tacki ness required to enablelaminations to adhere together. Tackiness is best ensured by thepresence of a high proportion of the polymer itself in the form of asolution. To produce the desired Wetting, toughness and tackiness withease of removal of the sheet from the bowl, it is convenient to form thedough-like mass from both an emulsion and a solution, and in these thepolymers or copolymers may be the same or different. Some of the solventmay be removed in the mixing, and to ensure the desired tackiness themixer may be heated towards the end of the mixing. The solvent forpolystyrene may be styrene itself. As the styrene is volatile some of itis lost but it appears to be polymerized to some extent during theprocess. Preferably the styrene is used in catalysed form, because thenit polymerizes faster, with the result that more of it is retained inpolymer form in the dough-like mass.

Homogeneous distribution of the fibers without degradation is important,and the dough-like mass should be formed in a mixer which Will notproduce excessive fiber degradation.

When polyvinyl chloride forms part of the polymeric constituent, it ispreferably introduced into the dough-like mass in particulate form. Itcan also be introduced as a dispersion, for example by mixing polyvinylchloride powder into the solution of the dissolved part of the polymerconstituent. Any antimony oxide to be present may also conveniently bemixed into this solution. Conveniently, the styrene may be present notas the simple homopolymer of styrene but as a copolymer with the diesterof maleic acid and a C alcohol sold under the trademark Alphanol or withsome other similar ester formed from an unsaturated dicarboxylic acidand an alcohol of medium chain length or a mixture of such alcoholssince the ester moiety acts as a plasticiser for the styrene.

The calender used in forming the sheet may be of the type comprising alarge steam-heated bowl and a smaller water-cooled bowl which can bemoved apart from one another. The dough-like mass is fed into the nip ofthe calender, and at the end of each revolution the distance between thebowls is increased, so that the mass is built up in laminations on thehot bowl to the required thickness.

The method of the invention is advantageous in that calendering thedough-like mass to sheet causes little or no degradation of the fibersto take place and leads to only a little alignment of the fibers, thusavoiding pronounced unidirectional strength. If, however, unidirectionalstrength is required some continuous glass filaments, such as thoseproduced by spinning a large number of monofilaments together, may befed into the nip of the calender to extend throughout the length of theresultant sheet, at the expense of some loss of mouldability. Eachlamination formed on the calender bowl must be very thin so that it willsubstantially dry before the next lamination is laid on it. Preferably,each lamination is from 0.0004 to 0.001 inch thick.

The sheet, as it comes from the calender, may contain voids and someresidual volatile constituents which may spoil the physical properties,translucency and general appearance. If so, it may be reheated andpressed to density and polish it. This is preferably done in a hydraulicpress, but may be done by passage through hot and cold rolls.

BRIEF DESCRIPTION OF THE DRAWINGS A rigid flat sheet according to theinvention is shown disposition of the fibers is visible), and

FIG. 1 shows a plan view of the sheet (assumed for the sake ofsimplicity to be partly transparent so that the desposition of thefibers is visible), and

FIG. 2 shows a section of the sheet shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The polymeric matrix of thesheet is indicated as 1, and reinforcing fibers are shown generally as2. In FIG. 1, it can be seen that the fibers are randomly oriented inthe plane of the sheet, and from FIG. 2 it is clear that all the fiberslie substantially parallel to the plane of the sheet. Various fibers,seen end-on in FIG. 2, are denoted 3.

Some examples will now be given.

EXAMPLE 1 2.5 parts of asbestos fiber of average length from 0.15 to0.20 inch were mixed for 15 minutes with 5 parts of a 50% aqueousemulsion of polystyrene (of 50% solids content) in a mixer fitted withcentral rotating spiked bars. When the fiber Was thoroughly wet, 2.5parts of polystyrene granules in solution in 5 parts of toluene wereadded and mixing was continued for 30 minutes. After this time, afurther 5.0 parts of polystyrene in 10 parts of toluene were added and,finally, 7.5 parts of A staple chopped glass rove was fed slowly intothe mixer. Mixing was continued for a further 30 minutes to make a totalof 75 minutes.

The dough-like mass produced was transferred to the nip of a calender asdescribed above. A sheet Was formed on the large bowl maintained at 140C. by opening the nip at the rate of 0.0004" per revolution, this beingeffected by means of a ratchet-and-pawl arrangement.

Final densification and polishing were effected by heating thecalendered sheet in an oven at 150 C. for minutes and pressing at 4 toneper square inch for 1 minute in a hydraulic press fitted withwater-cooled platens.

EXAMPLE 2 30 parts of short asbestos fiber were wetted with 130 parts ofan emulsion of a copolymer of styrene and maleate ester (the emulsioncontaining 50% solids) in a mixer, and then 45 parts of styrene with2.25 parts of benzoyl peroxide and 1.15 parts of tertiary-butylperbenzoate were added. Finally 30 parts of /2" chopped glass rovingwere worked into the mass in the mixer. The mass was formed into a sheetas in Example 1.

EXAMPLE 3 described above are as follows:

EXAMPLE 4 Parts Asbestos 30 chopped glass roving 30 Emulsion ofstyrene-butadiene copolymer (50% solids content) 50 Solution ofpolystyrene in toluene (40% sohds content) 60 EXAMPLE 5 Asbestos 50chopped glass roving 50 Emulsion of polystyrene (50% solids content) 100Polystyrene-butadiene copolymer 50 Dissolved in toluene 180 EXAMPLE 6Asbestos 50 A" chopped glass roving 50 Emulsion of polystyrene (50%solids content) 20 Polystyrene granules 75 Acrylonitrile-butadienecopolymer l5 Dissolved in toluene 18 EXAMPLE 7 Asbestos 50 /2" choppedglass roving 50 Emulsion of copolymer of styrene and di-Alphanol maleate100 Polystyrene dissolved in toluene (50% solution) 100 Toluene (asadditional wetting agent) 13 EXAMPLE 8 Asbestos 50 A" chopped glassroving 50 Emulsion of methylmethacrylate (30% solids content) 50Solution of copolymer of methylmethacrylate and ethylacrylate dissolvedin toluene (40% solids content) 190 Toluene (as additional wettingagent) 5 Sheets produced by the method have exhibited high tensile,compressive, fiexural and impact strengths, comparative figures forsheets in which the polymeric constituent was produced from styrene andbutadiene, and for similar unreinforced sheets, being given below.

Reinforced Unreinforced polystyrene polystyrene Tensile strength, p.s.i11, 300 7, 000 Compressive strength, p.s.i 20, 000 12, 000 Flexuralstrength, p.s.i 20, 300 12, 000 Impact strength, it. lb./inch 1 0. 6

A further example will now be given to show the preparation of a rigidsheet containing a minor proportion of polyvinyl chloride.

EXAMPLE 10 lbs. of a 60% solution in toluene of a copolymer of styreneand the diester of maleic acid and Alphanol, 1% lbs. of stearic acid, 43/2 lbs. polyvinyl chloride powder, 38 /2 lbs. pulverised talc as filler,2 /2 lbs. of a mixture of stabilisers for polyvinyl chloride, and 19lbs. of antimony oxide were mixed together for about 45 minutes to forma solution phase. An aqueous phase was formed by mixing 14 lbs. of anaqueous dispersion of pigment into lbs. of a 50% solid content aqueousemulsion of polystyrene. 174 lbs. of a mixture of grade 3 and grade 4asbestos fibers were mixed with about one third of the solution phase ina 5 pike mixer over about 50 minutes, and then the remainder of thesolution phase was added and mixed in for 5 to 10 minutes. The aqueousphase was then added and the mixing continued for 15 to 20 minutes toform a dough-like mass.

The dough-like mass was then transferred to the nip of a laminatingcalender of the type previously described. A sheet was formed on thelarge bowl, maintained at about C., by opening the nip at the rate of0.0004 inch per revolution by means of a ratchet-and-pawl device, untila sheet of the desired thickness was formed. Four sheets each 0.04 inchthick were then laminated together by pressing in a press at C.

The resultant laminated sheet is suitable for moulding purposes.

If desired, one or more surface layers may be laminated onto the sheetsto produce a decorative surface; the product is then suitable for use,for instance, as wall panelling. Thin, decorative or plain-surfacedfilms or sheets of thermoplastic material can be applied to thereinforced sheets, at the densification stage, to produce attractivedecorative surfaces, of improved weathering resistance, or merely tohide the visible fiber pattern on the reinforced sheets. Naturallypigments and fillers may also be included in the sheets, beingincorporated as required in the doughlike mass.

In the drawings, the polymeric matrix of the sheet is indicated as 1,and reinforcing fibers are shown generally as 2. FIG. 2 shows that allthe fibers lie substantially parallel to the plane of the sheet. Variousfibers, seen end-on in FIG. 2, are denoted 3.

What is claimed is:

1. A rigid sheet composed of a thermoplastic polymeric materialreinforced by lose fibers uniformly dispersed throughout the sheet andpredominantly randomly oriented and lying in the plane of the sheet,said polymeric material consisting essentially of a minor proportion ofa polymeric constituent selected from the group consisting ofhomopolymers and copolymers of vinyl chloride and 7 a major proportionof a polymeric constituent based on a monomer selected from the groupconsisting of styrene, methylmethacrylate and acrylonitrile, the fibersconstituting 20% to 60% by weight of the sheet.

2. A sheet as claimed in claim 1, in which the fibers are at leastpredominantly inorganic.

3. A sheet as claimed in claim 1, which comprises a plurality of layerslaminated together, the fibers being present in all, or a substantialnumber of successive laminations.

4. A sheet as claimed in claim 3, in which the fibers at leastpredominantly have a length greater than the thickness of thelaminations.

5. Arigid sheet according to claim 2, in which from 20 to 100% of theinorganic fibers are asbestos.

15 6. A rigid sheet according to claim 4, in which the fibers are amixture of asbestos and glass.

References Cited UNITED STATES PATENTS 1,877,651 9/1932 Eisenhardt16l170 8 2,315,503 4/ 1943 Crowell et al 260884 2,879,547 3/1959 Morris18-55 3,275,713 9/1966 Rubens et al. 260884 2,688,580 9/1954 Fingerhut161195X 3,022,210 2/ 1962 Philipps 161170X 3,121,446 2/1964 Richardsonet a1. 161-170X 3,133,825 5/1964 Rubens 161204X 3,188,263 6/ 1965Pilaumer 161-205X 3,257,266 6/1966 Sapper 161205X 3,301,739 1/1967Vanderbilt 264-137X FOREIGN PATENTS 607,756 9/ 1948 Great Britain260--884 629,669 10/ 1961 Canada 260884 ROBERT F. BURNETT, PrimaryExaminer R. O. LINKER, 111., Assistant Examiner US. Cl. X.R.

